The present invention relates to: a measuring steady rest for supporting and measuring central workpiece regions, in particular, bearing points on shaft parts, in particular, crankshafts; a grinding machine for grinding at least central workpiece regions, in particular, on crankshafts, with such a measuring steady rest; and a method for supporting and measuring central workpiece regions, in particular, on crankshafts, with such a measuring steady rest on such a grinding machine.
There are known steady rests for supporting central workpiece regions during machining of central and/or eccentric workpiece regions, in particular, bearing points on, in particular, crankshafts. These steady rests serve to additionally support so-called relatively soft workpieces, e.g., crankshafts, during the grinding in such a manner that introducing the grinding forces results in—to the greatest extent possible—no or at least very little deformation of the workpiece to be ground. In particular, with longer crankshafts, there therefore arises the need to adjust such steady rests during the grinding in order to receive the introduced grinding forces such that the grinding forces are distributed to the greatest extent possible at a plurality of main bearings of such a crankshaft, or, with other shaft parts, to the greatest extent possible at a plurality of points over the longitudinal extension thereof. Efforts to optimize the efficiency of the production process now usually involving using one or more grinding discs that grind at least partially in time-parallel the central shaft sections to be machined. Due to the limited space, therefore, use of a plurality of steady rests makes it difficult to provide yet another measurement device that, in terms of space, will collide with neither the grinding disc(s) nor the steady rests. One solution that, in this context, has been provided if measurements are to be taken during grinding is to interrupt the grinding process and then measure the currently-achieved diameter. This does not constitute actual in-process measurement. Often, steady rests from the company A OBOTECH Systems Inc are used on grinding machines for grinding crankshafts. These known steady rests usually have three jaws, which usually have a PCD (polycrystalline diamond) coating or CBN (cubic boron nitride) coating at the application against the bearing point. Steady rests having three jaws have an advantage in that each bearing point to be supported is “clamped”, so to speak. Thus, a workpiece is clamped in a self-centering manner in the position thereof, and the jaws are advanced in the direction of the workpiece center, i.e., centrically with respect to the diameter of the respective central workpiece section. The movements of the individual steady rest jaws are permanently mechanically coupled, which leads to a relatively complicated mechanical system. However, such steady rests only make sense to use if the bearing points to be machined have already been relatively well pre-machined so that the steady rest reliably abuts thereagainst and can support. Tracking the steady rest during the grinding process is therefore burdensome and difficult during production due to the aforementioned reasons. The permanent mechanical coupling of the three jaws of the known steady rest requires relatively significant forces to be assumed during infeeding, which may lead to pronounced track marks on the bearing point to be supported. So-called two-point steady rests, with which the supports are optionally also previously PCD-coated, are fed in with CNC axes. Use of two separate CNC axes further raises the construction complexity of such steady rests and thus the costs thereof. The two support points and/or support regions of such known two-point steady rests are usually arranged at right angles to each other, wherein one such steady rest is generally arranged opposite the grinding disc so that the grinding forces can be absorbed.
Steady rests with which two support points are arranged with positive control are already known, such as in U.S. Pat. No. 6,257,972 B1. The two supporting points of the known steady rest are supported against a third opposite supporting point. The individual steady rest support elements are either fastened by means of stops or installed at a finish-ground bearing. Tracking of the steady rest during grinding of the steady rest position is not intended and not even possible.
DE 10 2011 015 205 B3 also discloses a two-point steady rest having two supporting parts arranged fixedly relative to one another. Such a known steady rest is used to horizontally and vertically support a workpiece, and has two supporting members arranged at a lateral distance from each other that are adjustable with respect to the workpiece. Such known steady rests lead only to limited applications, at best only inadequately available for many of today's applications, especially with respect to the true-running accuracy that can be achieved. These known steady rests are alike in needing to be retracted not only for the purpose of loading and unloading a new workpiece due to the relatively large space requirements thereof, but also for the purpose of measurement. Separate measurement devices, which are usually pivoted relative to the workpiece region to be measured, have additional inaccuracies in the measurement result due to the movement members required therefor. What is more, true in-process measurements are hardly possible with such devices.
This is especially problematic either if deviations in the cylindricity are present in the longitudinal direction of the workpiece region to be measured/machined, or if there is a desire to measure precisely such inaccuracies, because in such instances, the measurement device must measure the component to be measured or the workpiece region to be measured at a plurality of planes adjacent to one another in the longitudinal direction. For grinding of shaft parts and, then, in particular, bearing points on crankshafts, measurement devices from, for example, the companies Marposs S.p.A. or also JENOPTIK Industrial Metrology German GmbH are often used.
DE 694 13 041 T2 also discloses a measurement sensor of the company Marposs S.p.A., for controlling linear sizes. This measuring device can be used to measure inner diameters of holes as well as outer diameters. A movable sensor in the form of a spherical element is provided for this purpose, wherein deflections are transmitted to the spherical element by means of an additional element. With this known measuring device, the spherical element is in contact with an abutment surface over which the element is movable in the oblique direction, wherein the abutment surface is concave in the cross-section thereof, this concavity serving as a seat for the spherical element and guiding same in the oblique direction.
DE 33 36 072 C2—which was also filed by the company Marposs S.p.A.—also describes a sensing device for measuring linear dimensions. Here, too, the measurement is performed with known sensing heads for measuring external dimensions as well as internal dimensions in one plane, perpendicular to the longitudinal axis of the finished workpiece region to be measured. However, there is no description of measuring shape deviations or profilings in the longitudinal direction of the central workpiece section.
In addition, the prospectus “MOVOLINE In-Prozess-Messtechnik” of the company Jenoptik describes such an in-process measurement technique for measuring machined workpiece regions, including continuously measuring these dimensions during machining in order to adaptively control the grinding process on the basis of the measured workpiece parameters, as well as optionally using these measurement devices in order to control the circularity (see the measurement systems DF500 or DF700, p. 15). With this known measurement system, there is also a description of working with two measuring heads in the sense of an in-process measurement in order to determine outer diameters. Even if the shape dimensions are measured after complication of the grinding or a grinding process step but are not used for adaptive control, then this measurement system, too, necessitates additional space, existing only to a limited extent on the grinding machine for such highly-complex components as a crankshaft.
Also known are steady rests with which already-known measurements can be performed on the workpiece to be supported. DE 102 09 371 A1 discloses a quick-centering steady rest in which a measurement system is arranged facing away from the actual support point of the steady rest, by means of which measurement system it is intended to be possible to indirectly measure the supported workpiece region. However, this requires first locking the measurement system in the respective spindle sleeve to null or to a base level, because of the centering after the steady rest has been placed against the surface of the workpiece.
DE 690 883 T2 also discloses a steady rest with remote measurement. The known steady rest entails a three-jaw steady rest with self-centering action, with which the respective jaws of the steady rest are connected via a linkage to a work body, longitudinal displacement thereof in turn constituting the actual measurement result of the supported workpiece region. Here, too, this therefore entails indirect measurement of the supported workpiece region, the accuracy of which is limited by the many intermediary movement members. Especially for today's pursuit of the highest accuracies with many workpieces to be produced, limits should be set first and foremost with use of in-process measurements with this known steady rest with remote measurement.
All of the known additional systems with grinding of, in particular, crankshafts, i.e., systems for additionally supporting, i.e., the steady rests, such as also systems for measuring preferably before or during the grinding, are alike in either requiring additional measurement devices or in only being able to perform measurements discontinuously. With known steady rests, the actually measurements can only be realized indirectly, which includes loss of measurement accuracy.